Modern computing systems, particularly as used with mobile computing devices such as smartphones, tablet computers, laptop computers, etc. may operate in what may be characterized as a “bursty” mode. A bursty mode of operation means that computing element such as a central processing unit (CPU), graphics processing units (GPU), system on a chip (SoC), network adaptors, radios, and/or other components alternate between an idle state in which they draw very little power and a full load state in which they draw relatively high amounts of power. As a consequence of these rapid swings in power requirements, the currents drawn by processors may also experience large transients. These large transient currents can result in significant voltage dips in the power supplies that regulate the voltage delivered to such components.
For example, a buck converter is a commonly used switching power supply. In its simplest form, a buck converter steps down an input DC voltage to a lower, regulated level delivered to a load using a switch, a diode, an inductor, and an output capacitor. Large transient currents like those discussed above can significantly discharge the output capacitor of the buck converter, reducing the output voltage, more quickly than the switch can ramp up the current through the inductor to meet the instantaneous current demand of the load. As a result, the output voltage can dip below a minimum acceptable level for the load.
To mitigate or reduce this voltage dip, system designers have historically been forced to choose from among various power supply design techniques that have the undesirable side effect of reducing the overall efficiency of the power supply. For example, the voltage dip may be mitigated by selecting a steady state operating voltage that is sufficiently high that even a worst case voltage dip will still result in an output voltage that is above the minimum requirement for the load. However, many losses in such systems are proportional to the square of the voltage, so even a small increase in steady state operating voltage can have a significant increase on overall losses and overall system efficiency. Another alternative is to reduce the inductance of the converter. However, all else being equal, a reduced inductance may require that the inductor be operated at a higher frequency to achieve the same net energy transfer to the load. This higher operating frequency can undesirably impact switching losses, again reducing overall system efficiency.
Thus, what is needed in the art is a way to reduce the transient voltage dip associated with large changes in load on an inductor-based (i.e., magnetic) switching converter without causing an undesirable reduction in the system's efficiency.